Pathogens are inhibited into entering into the body by various mechanisms such as:

  • The eye has tears and eyelashes
  • Respiratory system having mucus and cilia lining the tracts
  • The skin is a physical barrier including antibacterial properties of sebum and sweat

Immune System

  • The immune system is a collection of cells tissues and organs with mechanisms that defend an organism against the pathogen and other foreign substances.
  • An immune system response in the body is a complex series of specific and non-specific processes involving a range of cells and chemicals.


  • Non-specific immune response is the ‘general’ response to pathogen.
  • For example the physical barriers such as the skin and mucus.
  • Phagocytosis engulfs the pathogen regardless to what the pathogen is
  • The response is immediate as they are always present


  • Specific immune response is far flower however is unique to each pathogen
  • Cell mediated response in the T-cells
  • Humoral response in B-lymphocytes


  • An antigen is any part of an organism or substance that is recognised as a non-self (foreign) by the immune system and stimulates an immune response
  • Antigens are usually proteins that are part of the cell surface membrane or cell wall
  • The presence of a non-self antigen causes the production of an antibody as part of the body’s defence system


  • Lymphocytes are white blood cells
  • They are produced by stem cells


  • Matured in the bone marrow
  • Produces antibodies and antitoxins
  • Responds to foreign materials outside body cells
  • Humoral immunity (immunity involving antibodies that are present in the body’s fluids (humour) such as blood plasma)


  • Matured in the Thymus Gland
  • Responds to antigens presented by the phagocytes
  • Responds to viral infected cells and cancer
  • Associated with cell mediated immunity (immunity that involves body cells)

How lymphocytes recognise cells belonging to the body:

  • There are around 10 million different lymphocytes present at any time
  • In the foetus, these lymphocytes are constantly colliding with other cells. However infection as a foetus is rare
  • Lymphocytes will therefore collide almost exclusively with the body’s own material. Lymphocytes have receptors that exactly fit those of the body’s own cells.
  • These lymphocytes either die or are suppressed whether leaving those that might fit foreign antigens and therefore only respond to the presence of foreign materials
  • In adults lymphocytes are produced in the bone marrow only encounter self-antigens
  • Any lymphocyte that shows an immune response to the self-antigens undergo programmed cell death (Apoptosis)